a. Field of the Invention
The present invention pertains to devices for analyzing hydraulic characteristics of soil, and in particular, to an infiltrometer for automatically measuring water infiltration under tension.
b. Problems in the Art
Infiltrometers have been utilized for a number of years to attempt to derive soil characteristics. For example, an elementary infiltrometer is disclosed in "Measurement of Sorptivity in Soil Water Diffusivity in the Field" by Clothier and White, SOIL SCI. SOC. AM. J., Vol. 45, 1981, pgs. 241-245. The fundamental theory and structure of infiltrometers is described in this article, and it is incorporated by reference herein.
Infiltrometers have been found useful to measure soil characteristics and properties such as sorptivity, unsaturated hydraulic conductivity, and macroporosity, to name a few examples. Such measurements help derive information which is useful in determining characteristics such as soil hydraulic properties for studying leeching and erosion, modeling soil pore structure to estimate drainage and other characteristics, and allowing prediction of such things as root growth and other associated factors.
The type of infiltrometer portrayed in Clothier and Wilson is elementary and does have certain weaknesses and problems. For example, truly accurate and reliable measurement is difficult. The production of tension in the reservoir is many times erratic and measurement ranges are many times insufficient to be very useful, especially at low flow rates and low tensions.
Attempts have been made to improve upon these elementary infiltrometers. For example, as disclosed in Constantz and Murphy, "An Automated Technique For Flow Measurements From Marriotte Reservoirs" SOIL SCI. SOC. AM. J., Vol. 51, 1987, pgs. 252-254, incorporated by reference herein, one such attempt is described. Additionally, that article also describes the problems with other types of infiltrometer systems.
The Constantz and Murphy technique utilizes a pressure transducer at the top of the Marriotte column. Continuous pressure readings can be converted into changes in water level to derive the relevant measurements needed. This technique does have certain problems however.
First of all, there is room for improvement with regard to reliability of the data from this type of system. The bubbling action still creates erratic results affecting readings of the transducer. Especially at low flow rates and tension, these measurements must be very precise over the test periods. With only one transducer, a significant measurement error can exist due to tension fluctuations or "noise" caused by bubbling in the Marriotte column.
Such problems also impact upon how quickly the data can be obtained, and with respect to the ease of obtaining the relevant data. Of course, the better and more reliable the measurements, the better and more reliable the derivation of results regarding soil characteristics.
The present state of the art also has problems with regard to the flexibility of such testing systems. For example, there is room for improvement in whether and how tension can be varied in the Marriotte column. It is also advantageous to have a device which allows interchangeability of Marriotte columns.
It is therefore a principal object of the present invention to provide an automated tension infiltrometer which improves over or solves the deficiencies and problems in the art. A further object of the present invention is to provide an infiltrometer as above described which facilitates automated measurement of infiltration.
A further object of the present invention is to provide an infiltrometer as above described which allows easy and flexible interfacing with recording instrumentation and computing components to allow quick and reliable derivation of results for soil characteristics.
Another object of the present invention is to provide a means as above described which improves reliability and accuracy of measurements.
A still further object of the present invention is to provide a means as above described which is accurate and reliable even at low tensions and low flow rates.
A further object of the present invention is to provide a means as above described which can obtain more data than conventional systems.
Another object of the present invention is to provide a means as above described which can obtain measurements more quickly than conventional systems.
A further object of the present invention is to provide a means as above described which can be adjusted to operate reliably over a range of tensions.
A further object of the present invention is to provide a means and method as above described which allows interchangeability of components, such as Marriotte columns.
A further object of the present invention is to provide a means as above described which is efficient, convenient to use, and economical.
These and other objects, features, and advantages of the present invention will become more apparent with reference to the accompanying specification and claims.